Make using of the compiler single-thread

[vmishenev]

Dokka analyses Java and Kotlin code in multi-thread mode. ( see AsyncSourceToDocumentableTranslator and #2936)

Currently, the compiler is not thread-safe (see #1599, KT-58327) so we have a patch for the compiler like #3143
But we do not have a warranty that we patched everything or will not have new places in the future. It can lead to flaky analysis.

Possible solution

Make coroutines dispatcher single-thread.

[IgnatBeresnev]

Update after an internal discussion: цe'll test if there's any noticeable performance difference between single-threaded and mult-threaded runs and proceed if there isn't. If there is, we'll think how to mitigate it or avoid it for K1 altogether.

[vmishenev]

I measured Dokka performance in case of single-treaded calling compiler API/descriptors/PSI.
It was conducted on StdLib via CLI json (commit f98451e38169a833f60b87618db4602133e02cf2). The json configuration was got by a dump of Gradle runner.
The documentable model takes 16-20% more time to be generated in comparison with multi-threaded mode.
But it does not impact on total running time of Dokka since generating of documentable model takes 10% of overall running time, i.e. total impact ±2%.
So users will see no noticeable performance difference.

Some results: (the number of measurements=5)

Multi-thread			Single-thread
	Documentable model generating (sec)	Overall time (sec)		Documentable model generating (sec)	Overall time (sec)
_	56,005	515,93	_	72,506	556,85
_	56,092	576,65	_	69,625	549,12
_	56,385	587,15	_	67,859	519,21
_	57,059	592,63	_	67,504	558,76
_	55,216	537,96	_	66,345	539,11
Average	56,1514	562,064		68,7678	544,61